Datasheet

3
LT1776
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 40V, V
SW
open, V
CC
= 5V, V
C
= 1.4V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Timing
f Switching Frequency 180 200 220 kHz
● 170 230 kHz
Maximum Switch Duty Cycle ● 85 90 %
t
ON(MIN)
Minimum Switch On Time High dV/dt Mode, R
L
= 39Ω (Note 4) 300 ns
Boost Operation
V
C
Pin Boost Threshold 1.35 V
dV/dt Below Threshold 0.2 V/ns
dV/dt Above Threshold 1.6 V/ns
Sync Function
Minimum Sync Amplitude ● 1.5 2.2 V
Synchronization Range (Note 6) ● 250 400 kHz
SYNC Pin Input R 40 kΩ
SHDN Pin Function
V
SHDN
Shutdown Mode Threshold 0.5 V
● 0.2 0.8 V
Upper Lockout Threshold Switching Action On 1.260 V
Lower Lockout Threshold Switching Action Off 1.245 V
I
SHDN
Shutdown Pin Current V
SHDN
= 0V 12 20 µA
V
SHDN
= 1.25V 2.5 10 µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Control circuitry powered from V
CC
.
Note 3: Switch current limit is DC trimmed and tested in production.
Inductor dl/dt rate will cause a somewhat higher current limit in actual
application.
Note 4: Minimum switch on time is production tested with a 39Ω resistive
load to ground.
Note 5: Parts are guaranteed to survive 60V on V
IN
and V
SW
. However,
thermal constraints will limit V
IN
in some applications, depending primarily
on maximum output current and switching frequency. See Applications
section for more information.
Note 6: Internal oscillator is guaranteed to sync up to 400kHz. However,
thermal constraints and/or controllability issues may place a lower limit on
switching frequency in actual usage. See Applications section for more
information.